Cladistic analysis of the octopods based on anatomical characters

Abstract

Parsimony analysis of 29 tinned and finless octopod taxa considered 66 anatomical and morphological characters to discover synapomorphies that unite monophyletic groups. The resultant cladogram (177 equally parsimonious trees at 191 steps, CI 0.429) resolved all relationships except those among the 16 exemplars of the Octopodidae included and those among Tremoctopus, Ocythoe and Argonauta. Boot-strap values of over 90% support the monophyly of the tinned and finless octopods, relationships among the tinned octopods, the bolitaenids and the monophyly of Haliphron, Tremoctopus; Ocythoe and Argonauta; bootstrap values for other nodes range from 57 to 79%. Among tinned octopods, specimens representing Grimpoteuthis are basal, as Voss (1988a) suggested. Specimens of Opisthoteuthis represent a distinct lineage, and are sister taxon, in this analysis, of Cirroteuthis (although specimens of Stauroteuthis could not be included). New definitions of the genera Opisthoteuthis and Grimpoteuthis are provided to reflect their separate evolutionary histories rather than their overt morphological similarity. Among finless octopods, bolitaenids are basal. The monophyletic Octopodidae is the sister taxon to the clade containing the sister taxa Vitreledonella and Amphitretus, and Haliphron, Tremoctopus, Ocythoe and Argonauta. The Ctenoglossa and Heteroglossa, families grouped by shared radular dentition, are diphyletic and paraphyletic, respectively. The cladistic relationships demonstrate that both the Vitreledonellidae and Idioctopodidae are junior synonyms of the Amphitretidae; despite conspicuous morphological differences separating these taxa, they share a recent evolutionary history.